This invention relates generally to ignition coils, particularly for internal combustion engines, and vehicular ignition systems, and more specifically to a bobbin assembly of the ignition coil.
With the advent of the microprocessor and related sophisticated electronic controls, vehicular ignition systems and ignition system strategies have undergone a great many improvements. Some of the benefits now being derived through the incorporation of these new systems and strategies include improved spark timing, and improved reliability. One outcome, of a more efficient combustion process is that it allows for the extension of the percentage of exhaust gas recirculation. Improvements in emissions, power, and other performance characteristics result.
Changes in the ignition coil design have also been a part of this overall improvement. Use of the single ignition coil for each ignition device, i.e. spark plug, has provided the opportunity to more precisely control ignition characteristics within each combustion chamber. Some ignition systems for internal combustion engines use an ignition coil or coils having a C-shaped iron core within a non-conductive housing, with the primary and secondary windings wound on individual bobbins inter-nested within one another and lying within the boundaries of the C-shaped iron core. The coil is filled with epoxy potting material or other insulating material as a final step in the process. The epoxy material prevents the effects of torsional forces that the windings are subject to in operation. One effect of the torsional forces is that the insulation on the windings wears quickly.
One known method of filling the windings with epoxy is using a vacuum atmosphere around the windings and letting the epoxy impregnate from the outside of the coil to the inside of the coil. One drawback of such a method is that it may take many hours for the epoxy to penetrate into the coil windings. Another drawback is that if full penetration is not achieved the efficiency of the device decreases. There is in fact a delicate balancing of many factors to achieve perfect impregnation, namely the chemical reaction time of the epoxy, winding tension vacuum level, and processing temperatures. The ideal situation occurs when the windings impregnate uniformly in the least amount of time with the cured epoxy exhibiting the desired physical properties. Attempts have been made to reduce the impregnation time by varying certain constituents of the epoxy formulation as well as certain manufacturing processing parameters. However, none of these methods significantly reduced the impregnation time.
U.S. Pat. No. 3,377,602 describes another method of impregnating a coil with a resinous material. In that patent the resinous material is forced with positive pressure through a single circumferential groove in the interior of a two-piece pole portion upon which wire is wound. The patent teaches away from using a vacuum environment. The oils and moisture remaining in the windings will inhibit the distribution of resinous material resulting in an uneven distribution of material throughout the winding. This method of fastening the windings uses a felt member which also must become saturated in epoxy in order to hold the windings.
It would therefore be desirable to provide a method of impregnating coil windings with epoxy evenly through its entire cross section in a relatively short period of time.